The Association of Higher Civil and Public Servants' Executive Committee took the decision at a meeting yesterday.

The move is a blow to the Government as the union has traditionally backed national agreements.

However, it is a small union and has just 32 votes out of the total public sector unions' vote of 2,890, so its decision will not topple the prospect of a deal.

The proposed agreement would mean its members, whose earnings range from around €61,000 to over €100,000, will face pay cuts of over 5.5pc. They would also face an increment freeze over the next three years.

The union's general secretary, Dave Thomas, said the decision was not taken lightly. He said members had already suffered a range of cuts recently, which included pay cuts of between 15pc and 17pc before tax and Universal Social Charge hikes are counted.

Meanwhile, a union for 12,000 lower-paid civil servants, the CPSU, which walked out of negotiations on an agreement earlier this week, will launch a campaign against the cuts today.

Members from around the country will outline details of their 'Nothing More to Give' campaign, claiming they cannot cope with further cuts to their disposable income.

A group representing 70,000 frontline workers, who are opposing the deal, will meet in Croke Park tomorrow.